To address the issues of large footprint, complex configuration, and lack of flexibility in switching associated with traditional passive filters in high-voltage direct current (HVDC) systems, this paper proposes a hybrid active power filter (HAPF) solution. The HAPF integrates a passive filter and a voltage source converter (VSC) in series, employing two control strategies: current control to compensate harmonic currents and impedance control to enhance low-impedance filtering performance. One HAPF is capable to filter multiple harmonics, and can reach a filtering rate 95

特高压直流输送高比例清洁能源,系统扰动时的过电压问题是制约直流输送能力的关键因素.针对传统比例积分电流控制器的不足,提出一种基于预测直流电流变化趋势的动态参数控制方法,并结合低压限流环节参数优化,明显改善了换相失败期间送端交流系统的低电压和过电压现象.该方法经过实时仿真试验以及现场调试验证,已应用于青海–河南等特高压直流工程中,有效地抑制了暂态故障下的交流过电压,改善了故障恢复期间直流系统性能,有效提升了新能源外送比例.

UHVDC transmission technology has been widely used in China. However, the commutation failure of multi-infeed HVDC systems has been a persistent issue affecting the safe and stable operation of large power grids. To address this problem, a converter based on the integrated gate commutated thyristor (IGCT) is proposed. By conducting a detailed analysis of the topology and commutation process of the IGCT converter, as well as comparing the steady-state and transient performance with a thyristor converter, it has been verified that the IGCT converter can effectively prevent commutation failure by actively turning off the current. This research paper reveals the principle of commutation area invariance in line commutation converters and offers a new direction for the application of IGCT in HVDC transmission technology. These findings hold significant theoretical and practical significance for establishing a safer, more efficient, and higher-power HVDC transmission system.

Hybrid cascaded ultra-high voltage dc is a new dc technique with a line commutated converter cascaded with one or several voltage source converters. It is an effective solution for large capability transmission as well as improving the stability of the ac grid with multiple dc transmission systems feeding in. Baihetan-jiangsu dc project in China is the first cascaded ultra-high voltage dc project in the world. For a receiving end with a strong ac system, the short circuit current is always large and close to the maximum ac breaker breaking capability, which is a threat to the ac system fault clearance. In this paper, the issue of excessive short circuit current in a hybrid cascaded ultra-high voltage dc system is discussed and revealed. The process of the short circuit current developing is divided into 2 stages. Characteristics and the calculation method of the short circuit are proposed, and based on this, a control method is proposed, which can suppress the short circuit current during the fault clearance effectively. The parameter setting method is proposed. Finally, based on the scenario of the Baihetan-jiangsu dc project, the strategy and the parameters setting method are validated under PSCAD/EMTDC.

提出了同站布置的混合级联特高压直流输电技术,并设计了该拓扑的直流滤波器、可控避雷器和快速旁路开关等关键设备及混合级联协调控制策略.为验证该技术的工程可行性,搭建了含真实一次和二次系统的低电压等级的动模平台,该动模平台不仅包含直流线路、换流阀、换流变、控保装置等常规直流设备,而且包含可控避雷器和快速旁路开关等特有设备,可准确模拟出该拓扑的实际特性.在动模平台上验证了系统的启停、阀组投退、故障穿越特性,动模平台的试验结果表明,混合级联直流方案启停平滑、运行方式灵活、故障穿越可靠,符合设计指标,具备工程可行性.

This paper proposes a novel AC filter system for a line commutated converter high voltage DC (LCC-HVDC) transmission system. Through the coordination of the hybrid active power filters (APF) and the existing reactive compensation devices, the proposed filter system can not only enhance the suppression performance for LCC-HVDC harmonics, but also optimize the AC yard layout with reduced reactive power sub-banks, reducing the cost of HVDC projects. The novel filter system adopts a serial passive resonance topology obtained by careful comparison of different APFs. A proper control scheme is then designed integrating the control strategy of the APF and impedance characteristics of the HVDC system, which is able to realize harmonic suppression and dynamic reactive power support simultaneously. In addition, a novel self-adaption digital low-pass filter algorithm is presented, which is used in the APF harmonic detecting step, enhancing both high precision and fast dynamic response. On the basis of a real HVDC project, the advantages of proposed filter system in harmonic suppression, reactive power regulation, and sub-banks reduction are simulated and demonstrated.

采用三次谐波注入策略可有效提高模块化多电平换流器(modular multilevel converter,MMC)的直流电压利用率,从而减小换流器的稳态和暂态电流应力,降低换流器的损耗,提高换流器的安全裕度和故障穿越能力.针对采用三次谐波注入策略的MMC,分析了子模块电容电压、桥臂电流、桥臂电压的主要谐波分量;通过将各次主要谐波分量表示为相量,最终建立了16阶MMC动态相量模型,然后将其线性化建立了小信号分析模型.所建模型可方便地与直流侧、交流侧以及控制系统进行接口,适用于采用三次谐波注入策略的MMC稳态解析分析和小信号稳定性分析.通过在PSCAD下建立电磁暂态仿真模型并对比仿真结果和解析计算结果,验证了所建立模型的精确性.

In the electromagnetic transient analysis of the power system, the frequency-dependent characteristics of the overhead line model parameters will have a significant impact on the calculation results. A novel method for calculating the ground return impedance of overhead transmission lines with the frequency-dependent characteristics is proposed in this paper. In this method, the non-integrable part of Carson formula is converted into integrable function by function substitution method, and the closed-form solution of ground return impedance is obtained, which is close to the calculation result of Carson formula. The accuracy of this method is much better than that of other approximation formulas. It can be used to improve the accuracy of ground return impedance calculation.

在双极-地制的特高压直流输电系统中,存在一极线路接地故障导致另一极保护误动、换相失败和过电压等情况,不利于直流的安全可靠运行.从理论上分析了单极接地故障扰动在极间的传递机理,以及直流输电电压对故障传递的影响,并通过电磁暂态仿真再现了故障的发展进程.指出,故障电流变化率较高是导致异常现象的根本因素,并且随着电压等级的提高极间耦合更加严重,建议电压等级较高的直流工程应特别关注极间耦合带来的问题,采取相应措施,提高特高压直流系统的可靠性.

特高压±800千伏直流输电技术作为世界上电压最高、容量最高(可达1000万千瓦级)、经济输电距离最远(可达2000公里级)的直流输电技术,可以跨越千里之外,将集中了80％以上能源分布的中西部和北部地区的电力,传输到集中了70％以上电力消费的东部和中部地区.该技术之所以具备这样的优势,是因为直流电压的提高可以大幅降低输电损耗,进而提升经济输电距离和输电走廊利用效率.但这也带来了相当大的挑战:电压和电流的提升使得外绝缘设计、电磁环境控制以及装备研制的难度大幅提升.

特高压直流受端分层接入500kV/1000kV交流系统的接线方式在世界上属于首创,系统设计及运行均无可借鉴的经验。分析了受端分层接入方式对控制保护的影响,以及引入高、低端换流器中点分压器电压测点的必要性。为了防止因测点增加而降低直流系统运行可靠性,分析了中点分压器可能出现的故障类型,提出了中点分压器在各种故障情况下的控制保护动作策略。使用该策略能够保证在中点分压器故障时,直流系统不因控制系统动作而闭锁换流器。采用实时数字仿真验证了所提控制保护策略的正确性和可行性。研究成果已应用于在建的分层接入特高压直流工程。

Based on completely mastering ±800 kV transmission technologies, the first ±1100 kV direct current (DC) transmission demonstration project is being constructed in China. Combining theoretical analysis and a large number of experiments, the margin of switching overvoltage in converter stations, the configuration scheme and performance of lightning arresters, the shielding angles of ground lines under different geographical conditions, and the maximum air gap of lines have been determined. The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided. The external insulation is designed differently for light, medium, and heavy pollution areas. For the ±1100 kV project, if the 8 × 1250 mm2 conductors are applied, the pole gap is 26 m and the height of the line is 25 m, all the electromagnetic parameters will meet the requirement of international electromagnetic standards. The key design points of ±1100 kV converter transformers, smoothing reactors, converter valves, and wall bushings are researched and the 75 mH smoothing reactors, ±1100 kV/5000 A converter valves, and ±1100 kV/5523 A wall bushings are successfully made. The optimised hierarchical connection modes and coordination control measure of the ±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.

当高压直流(HVDC)整流站主要输送配套火电基地电力时,利用高压直流附加控制抑制次同步振荡(SSO)是一种经济有效的措施.基于单机和高压直流的简化模型,分析了整流站直流电流控制器(CCA)电流偏差增益对发电机次同步电气阻尼的影响,提出动态改变控制器增益抑制次同步振荡的控制策略及其工程实现方法.该方法通过优化直流电流控制器动态响应特性,改善了直流控制器在次同步频率范围内的阻尼.算例证明该算法可以快速抑制发电机次同步振荡,同时对直流系统原有的动态性能和暂态响应没有影响.与目前工程中应用的附加阻尼控制器相比,该方法实现简便,抑制效果好.

基于模块化多电平换流器的柔性直流系统当采用对称单极接线时,由于没有明显的直流中性母线提供直流侧零电位参考点从而需要附加接地方式.为了给柔性直流系统的接地方式选择提供依据,着重分析了各种接地方式的特点及适用范围,及其在多端柔性直流系统中的应用.然后,分析了不同接地方式下网侧零序电气量(例如电压和电流)向阀侧传播的机理;以及不同接地方式下阀侧零序电气量向变压器侧及直流侧传播的机理.以变压器采用Y0/Yn/△接线的实际柔性直流工程为例,对零序电气量传播机理进行了验证.结果表明,当交流系统发生不对称接地故障后变压器第3绕组可有效地屏蔽流入桥臂的零序电流;当桥臂上引入零序电压时变压器第3绕组对网侧绕组零序电流的屏蔽效果取决于变压器网侧通路零序阻抗和变压器第3绕组零序阻抗的比例.

为研究五端运行方式下换流站闭锁并打开交流进线开关后直流系统的放电特性,首先研究了舟山工程主接线、运行方式及设备参数,然后在此基础上对直流系统放电回路和放电过程进行分析,并计算出各种工况下直流系统的放电时间.同时,在PSCAD/EMTDC中建立了简化的五端柔直系统仿真模型,并对应理论计算工况进行仿真研究,得到各种工况下直流系统放电时间的仿真值,进而与特定情况下的现场数据进行对比.最后,综合理论分析和仿真结果,确定了换流站闭锁后直流系统放电至安全电压的时间约15 min.该计算方法也可用在其他的柔直工程中.

For UHVDC projects,it's determined by system harmonic characteristics whether low-frequency block-filters or DC-filters are needed to be installed or not.Firstly,based on two basic DC circuit "pole-pole"/"poles-earth" structures and calculation methods of line impedance per-unit,bipolar equivalent parameters considering overhead ground wires were obtained in detail;Then an optimal fitting method to approach original Carson integral results was proposed,with the equivalent wave impedance results of two DC circuit structures,the DC line harmonic impedance of different frequency was derived;Finally,depending on field-test DC line impedance results of the Lingzhou-Shaoxing ±800kV UHVDC project,as well as original Carson integral calculation results,the correctness of distribute parameters obtained and the accuracy of optimal fitting method were further demonstrated.

特高压直流输电工程输送容量大、送电距离远,其安全、可靠运行具有重要的现实意义。该文建立了并联换流器特高压直流输电系统的"故障树"模型,可以有效计算特高压直流输电系统的强迫能量不可用率和单、双极停运次数等可靠性指标;然后,提出了一种新的反映设备影响系统可靠性的灵敏度指标,可以有效发现钳制系统可靠运行的薄弱环节。最后,基于国家电网公司近10年的直流工程可靠性运行统计数据,对3种并联换流器特高压直流输电系统主接线方案,进行了可靠性指标计算和对比分析,并完成了设备影响系统可靠性指标的灵敏度分析,确定了影响系统强迫能量不可用率和单、双极停运次数的关键环节。结果表明,本研究能够确定可靠性高的并联换流器特高压直流输电系统拓扑结构,可以为提高特高压直流工程的可靠性提供重要的参考信息。

UHVDC project with hierarchical connection to 500 kV/1000 kV AC systems in receiving end is creative worldwide.There is no existing experience for this kind of DC control and protection.This paper studied control and protection scheme systematically.Special requirement on DC control and protection for UHVDC project with hierarchical connection to 500kV/1000kV AC systems in receiving end was analyzed.Hierarchical structure and function configuration of DC control and protection was presented.DC control strategy difference between normal power and reverse power operations was analyzed.DC control strategy adaptable to both normal and reverse operation was put forward.Key functions such as voltage balance between two 12-pulse converters,tap changer control,reactive power control,power transfer and distribution were studied.Its principle and implementation was presented.DC protection area allocation and function configuration for hierarchical connection DC system was promoted and variation with previous UHVDC project was compared.Measurement configuration of DC yard was analyzed.Study achievement was put into use in such kind of UHVDC project under construction.

特高压直流直接接入交流750 kV电网,对投切交流滤波器小组的断路器的耐压能力提出了严苛的要求,因此需要研究断路器的容性恢复电压水平。分析了交流滤波器小组断路器面临的各种交流故障工况,通过PSCAD软件建立了容性恢复电压的仿真计算模型,并以灵绍特高压直流工程为例计算得出了800 kV交流滤波器小组断路器的容性恢复电压最大值。仿真结果表明交流滤波器小组断路器的容性恢复电压由交流系统的短路水平和交流侧绝缘水平的影响决定,而且容性恢复电压超过了现有标准的要求,需研制适应工程需求的新型断路器。

特高压直流输电系统具有电压等级高、输送容量大、输电距离远、运行控制灵活等特点.数量众多的±800kV直流输电工程相继建成投运和持续安全稳定运行,标志着特高压直流输电技术已经成熟,具备大规模应用的条件.针对特高压直流输电系统对环境以及电网安全的影响等焦点问题,在总结国内外特高压直流输电技术特点的基础上,阐述了特高压直流输电系统规划设计中应关注的站址选择、环境影响、技术方案、安全稳定等方面的关键问题和解决思路,以提高工程的经济性和电网运行的可靠性.研究表明,伴随着电力电子技术的快速发展,特高压直流输电作为一种成熟适用技术,其电压等级、输电规模将进一步提升,新型换流技术的应用也将成为可能.